Volicitin

Some lepidopteran larvae and grasshoppers have been shown to induce plants on which they are feeding to release volatiles (mostly terpenes) that attract predators and parasitoids of the plant-eating insects, by the saliva or regurgitated juices from the mouths of the larvae. The cause in at least one insect, Spodoptera exigua, feeding on corn seedlings, is called volicitin, an elicitor of plant volatiles. Volicitin has been identified as A^-(175-hydroxylinolenyl)-L-glutamine (Figure 9.24). The linolenic acid, taken from the plant, is hydroxylated by the insect and conjugated with glutamine. The saliva also contains 17-hydroxylinolenic acid, 17-hydroxylinoleic acid, linolenyl-glutamine and linoleyl-glutamine, but none of these show activity comparable to volicitin. There does not seem to be any obvious benefit to the Spodoptera, nor is it clear how different insect species affect the bouquet of plant volatiles differently, so that parasitic wasps, specific to that insect, are attracted. Probably other compounds, with action similar to volicitin, will be isolated. The subject is new and more will be learned as research progresses.

Figure 9.24 Volicitin, a derivative of linolenic acid from a plant and glutamine from the insect, which stimulates the plant to release volatile compounds that attract predators of the insect

Figure 9.24 Volicitin, a derivative of linolenic acid from a plant and glutamine from the insect, which stimulates the plant to release volatile compounds that attract predators of the insect volicitin volicitin